This invention relates to an apparatus and method for determining the specific gravity of materials and more specifically to a method and apparatus for measuring the specific gravity of gemstones and the like.
An important aspect of the trade of a jeweler or a gemologist resides in the ability to determine the identity and value of a gemstone. While numerous parameters require analysis in the determination of a stone's identity, such as, the color, weight, flaw characteristics, and the like, one of the more important physical characteristics used in evaluating a gemstone is its specific gravity. This particular measurement is important because specific gravities of the major gemstones seldom overlap. Hence, this measurement provides a useful tool in distinguishing among differing types of gemstones and identifying counterfeit or synthetic gemstones.
While several techniques to measure specific gravity of gemstones have been developed in the past, most importantly, the use of heavy liquids and the hydrostatic process, jewelers and other persons desiring to measure specific gravity have thus far not been able to apply these methods in a sufficiently accurate fashion to make the specific gravity an accurate tool for analyzing the gemstone. Problems such as expense, difficulty in performing the measurements, and inaccuracy have made these techniques prohibitive for normal use at the retail level. A description of these heavy liquid and hydrostatic techniques may be found in R. Webster, Gems 566-82 (3ed. 1975), and the review of this material demonstrates the difficulties a jeweler would encounter in attempting to measure specific gravity of a gemstone according to these processes.
While the hydrostatic method typically yields a measurement having a greater accuracy than the heavy liquid method, this method needs a very sensitive balance, substantial calculation and substantial time in performance. A drawback of the hydrostatic method is that it is not effective in measuring the specific gravity of smaller specimens. The reason for this drawback is that the drag factor caused by the surface tension of the water can introduce substantial error in the measurement of specific gravity, particularly where the gemstone weighs less than five carats. This weight category includes a large majority of all gemstones. A quicker, though less accurate measurement for smaller gemstones can be made using a heavy liquid floatation method. However, due to the high density of the liquids required for this approach, a disadvantage is introduced since many of the high density liquids are poisonous and expensive. In addition, the heavy liquid method yields only a specific gravity range and not an exact value for the gemstone tested.
As a result of the difficulties referred to above, there is a need for an inexpensive yet accurate apparatus and method for determining the specific gravity of a gemstone with this apparatus being of a nature susceptible to utilization by a person untrained in sophisticated techniques for specific gravity measurement.